In dangerous zones such as rooms or plants with the industrial machines installed therein, the provision of a lock system is required for locking the machine drive at incomplete closure of the door to the dangerous zone in order that trouble of injury of an operator getting caught in the machine is obviated.
As such a lock system, there has been proposed to the art a safety switch assembly of an arrangement shown in FIGS. 16 to 26.
The safety switch assembly is electrically connected to an industrial machine installed in a room and consists of a switch body 101 and an actuator 102, as shown in FIGS. 16 to 18. The switch body 101 is secured to a wall surface near a doorway to the room, whereas the actuator 102 is secured to a door 103. The actuator is positioned in corresponding relation to a slot 101a of the switch body 101 so as to enter an operation section 111 of the switch body 101 when the door 103 is closed.
The ingress of the actuator 102 closes a connection contact of a contact block 9 incorporated in a switch section 112, thereby providing power supply to the machine in the room for machine drive. When, on the other hand, the door 103 is opened to remove the actuator 102 from the operation section 111, the operation section 111 returns to its initial state with the open connection contact of the contact block 9, thereby shutting off the power to the machine.
As shown in FIG. 16, the actuator 102 consists of a pressure piece 121 and a pair of support pieces 122, 123 supporting the pressure piece. The pressure piece 121 is formed with projected pressure faces 121b, 121b at opposite ends thereof and a depressed pressure face 121a interposed therebetween.
Next, description will be made on the arrangement of the operation section 111. As shown in FIGS. 19 to 23, the operation section 111 includes a drive cam 1 in the center thereof, which is rotatably carried by a support frame 11 via a cam shaft 4 for moving an operative rod 8 of the switch section 112.
The drive cam 1 is formed with rectangular recesses 1a, 1b in its outer periphery for receiving the pressure piece 121 of the actuator 102, the recesses adapted to correspond to a slot 101a or 101b. The drive cam 1 is also formed with a cam groove 1c on the opposite side from the recesses 1a, 1b with respect to the cam shaft 4. A cam follower pin 6 is inserted through the cam groove 1c.
Opposite ends of the cam follower pin 6 reach the proximity of the support frame 11 and are supported by guide grooves 7a, 7b of pin guides 7, respectively. The guide grooves 7a, 7b serve to limit the movement of the cam follower pin 6 in one direction and are formed along straight lines each extending through the center of the cam shaft 4 and parallel to the movement of the operative rod 8.
The cam follower pin 6 is coupled to an end of the operative rod 8 so that the movement of the cam follower pin 6 causes the operative rod 8 to move forward or backward to switch the connection contact of the switch section 112 between a closed position and an open position.
The actuator is provided with control plates 2, 3 on lateral sides thereof. The pair of control plates 2, 3 are disposed in corresponding relation to the projected pressure faces 121b, 121b of the actuator 102 and are rotatably carried by the cam shaft 4. Torsion coil springs 5, 5 are mounted to respective places between the control plates 2, 3 and the support frame 11 (shown in FIGS. 19 and 20) for returning the control plates 2, 3 to their respective initial positions. The torsion coil spring 5, 5 has one end thereof fixed to the support frame 1 and the other to the control plate 2, 3.
The control plates 2, 3 are each formed with a relief hole 2a, 3a, an edge of which is defined with a notch 2b, 3b for restricting the movement of the cam follower pin 6.
The notch 2b, 3b is cut into a semi-circular shape to receive the cam follower pin 6, as shown in FIG. 23. When the control plate 2, 3 is in the initial state (shown in FIGS. 20 and 21), the notch is positioned ahead of the cam follower pin 6 with respect of the movement thereof, as shown in FIG. 24A.
In the above arrangement, the drive cam 1 and the control plates 2, 3 in the initial state shown in FIGS. 20 and 21 are located in such a positional relation as to produce a rotational phase difference corresponding to a level difference between the depressed pressure face 121a and the projected pressure faces 121b, 121b of the actuator 102.
Now referring to FIGS. 24A, 24B and 24C, the operations will be described. Incidentally, although FIGS. 24A to 24C omits the reference character 3 for the unillustrated control plate on the left side as viewed from the slot 101a of the operation section 111, the control plate will be represented as "2, 3" herein because the pair of control plates operate in the same manner in this embodiment.
When the actuator 102 enters an interior of the operation section 111 through the slot 101a, the depressed pressure face 121a and projected pressure faces 121b, 121b at a distal end thereof first come into contact with the drive cam 1 and the control plates 2, 3, respectively (see FIGS. 24a). At this point of time, the cam follower pin 6 is not moved, staying at a cam-shaft-side end of the cam groove 1c of the drive cam 1.
Further ingress of the actuator 102 brings the drive cam 1 and control plates 2, 3 into rotation to advance the cam follower pin 6 along the cam groove 1c and to displace the notches 2b, 3b of the control plates 2, 3 out of the travel path of the follower pin 6 (see FIG. 24B). Subsequently, when the actuator 102 is further advanced to an insertion end, the connection contact of the switch section 112 is closed while the pressure piece 121 of the actuator 102 is fit in the recess 1a of the drive cam 1, as shown in FIG. 24C.
When the control plates 2, 3 are rotated in the above operations, the torsion coil springs 5, 5 are twisted in the direction of rotation so that the control plates 2, 3 are subject to a torque in the opposite direction to the rotation (returning force) resulting from the resilient force of the springs.
In removal of the actuator 102 from the position shown in FIG. 24C, the pressure piece thereof 121 pushes an inside surface of the recess 1a thereby bringing the drive cam 1 into the reverse rotation of that during the ingress of the actuator. This permits the operative rod 8 to retreat, returning the connection contact to its initial position (open) while the recess 1a of the drive cam 1 returns to its initial position shown in FIG. 24A. On the other hand, the control plates 2, 3 are urged back to their initial positions by the torsion coil springs 5,5, thus replacing the pin-lock notches 2b, 3b on the travel path for the cam follower pin 6.
Although the operations of the operation section are described by way of example where the actuator 102 is inserted in the slot 101a on a front side of the operation section 111, which include the two slots 101a and 101b. However, when the actuator 102 is inserted in the slot 101b on a top side of the operation section 111, the same operations as shown in FIGS. 24A to 24C take place. That is, the drive cam 1 and control plates 2, 3 are rotated to advance the operative rod 8 thereby switching the connection contact while the pressure piece 121 of the actuator 102 is fitted in the recess 1b of the drive cam 1.
At this time, any attempt to rotate the drive cam 1 with an operating plate (such as a screwdriver or the like) other than the dedicated actuator 102 is disabled by the control plates 2, 3.
When a pressure plate D is inserted through a central portion of the slot 101a (or 10b) to be pressed against the recess 1a (or 1b ) of the drive cam 1, as shown in FIG. 25A, the drive cam is rotated a little as shown in FIG. 25B. However, when the pressure plate D approaches the control plates 2, 3, the notches 2b, 3b of the control plates control the forward movement of the cam follower pin 6 while the guide grooves 7a, 7a of the pin guides 7 hold the cam follower pin 6, controlling the movement thereof in the rotation direction. Thus, the cam follower pin 6 cannot move forward nor in the rotation direction, disabling the rotation of the drive cam 1.
Even if both or either of the control plates 2, 3 is rotated using the pressure plate D, the drive cam 1 never rotates. In the initial state of the drive cam 1 and control plates 2, 3 as shown in FIG. 26A, the cam follower pin 6 is positioned out of interference with the notches 2b, 3b of the control plates 2, 3. Therefore, as shown in FIG. 26B, the attempt to rotate the control plates 2, 3 by pushing them with the pressure plate D only results in the rotation of the control plates 2, 3 alone while the drive cam 1 stands still with no force applied thereto.
In the safety switch assembly, the drive cam 1 is adapted to rotate to switch the connection contact of the contact block 9 incorporated in the switch section 112 only when the depressed pressure face 121a and projected pressure faces 121b, 121b of the actuator 102 substantially simultaneously press the drive cam 1 and the control plates 2, 3 on the opposite sides thereof. Hence, even if an attempt to rotate the drive cam 1 is made by inserting a tool with a flat tip, such as a screwdriver, into the operation section 111, the rotation of the drive cam 1 is prevented for inhibition of the operation of the operation section 111.
However, a problem exists with the arrangement wherein the ingress of the actuator into the operation section 111 enables the drive of the machine in the room but the egress of the actuator 102 from the operation section 111 at the opening of the door 103 returns the operation section 111 to its initial state to shut off the power to the machine whereby the operator is allowed to enter the room. That is, the arrangement involves fear that if a third person unaware of the presence of the operator in the room inadvertently closes the door 103, the actuator 102 is re-inserted in the operation section 111 to enable the drive of the machine in the room in which the operator is locked.
The conventional safety switch assembly mentioned above involves the possibility of occurrence of such an event because the ON/OFF control of the power supply to the industrial machine in the room depends upon whether the actuator 102 is inserted in the operation section 111 or not.
The invention contemplates the solution to the above problem and is directed to prevent the inadvertent closure of the door or the like from enabling the power supply to the industrial machine in the presence of the operator in the dangerous zone and to prevent the operator from being locked in the dangerous zone.